The following publications are representative of the most relevant prior art known to applicants at the time of filing of the application.
______________________________________ U.S. PATS. 2,526,073 October 17, 1950 Gardner 2,699,409 January 11, 1955 Hashimoto 2,728,733 December 7, 1955 Hashimoto 3,203,813 August 31, 1965 Gajardo et al. 4,446,040 May 1, 1984 Samanta Other Publication GB 2,118,463A November 2, 1983 Conti ______________________________________
Denim clothing, particularly jeans, is sometimes artificially aged during its manufacture to provide it with appearance, softness, and other such characteristics as may be dictated by prevailing fashion and marketing requirements. One currently popular aging process entails "stone washing" the denim as a part of the fabric finishing operation. This is conventionally performed by subjecting the denim fabric to a laundering and tumbling procedure in the presence of pumice stones to produce an abrasive action that serves to soften the fabric and also modify its appearance. Pumice has been used in this process since it is an inexpensive naturally occurring mildly abrasive material. However, pumice suffers from two major defects, i.e. (i) it is so friable that it may easily be crushed by hand and (ii) it is a natural product having such inconsistencies in strength, size, and shape that they effect its reproducibility in use. The friability problem means that, during stone washing, the pumice stones are rapidly abraded to such a small size that they become ineffective for further fabric finishing operations. In addition, the abraded pumice particles are often carried away with the wash water and, as a result, both clog drains and sewage systems, and get deposited into the pockets of the denim articles being treated, which deposits are removed before sale of the articles. The non-uniformity of the pumice serves to complicate the finishing process and make finishing to a constant appearance well nigh impossible.
British Application 2,118,463A discloses an abrasive rolling member for use in a denim finishing operation. The member is described as being "made of artificial pumice having vitrified inclusions formed therein and has either a cylindrical shape . . . or has a spherical shape." The document contains no additional explanation as to what is meant by the phrase "artificial pumice." But since pumice is a porous volcanic glass, "artificial pumice" would appear to mean a man-made version of pumice in which various molten silicates are cooled under pressure and then fused in a crucible.
U.S. Pat. Nos. 2,526,073, 2,699,409, and 2,728,733 show building materials formed from mixtures of expanded perlite and clay which are fired at a high temperature. There are no disclosures of using these materials in fabric finishing operations and the properties required for a building material are decidedly different than those for an abrasive rolling member used for stone washing.
U.S. Pat. Nos. 3,203,813 and 4,446,040 show insulating materials formed of perlite and clay which are dried at a comparatively low temperature and which may subsequently be exposed to a high temperature. There are no disclosures of using these materials in fabric finishing operations and the properties required for an insulating material are decidedly different than those for an abrasive rolling member used for stone washing.
Thus the prior art teaches the use of pumice, either natural or man-made, as the abrasive rolling member or stone in fabric finishing operations. While man-made pumice overcomes some of the non-uniformity and friability problems of the natural material, there is still need for considerable improvement. Accordingly, there is a need for an improved abrasive stone for use in fabric finishing operations. It is an object of the present invention to produce such an improved stone. It is a further object of this invention to utilize the improved member in fabric finishing operations.